Viral lifecycle entry and exit L14

Question 1

overview of viral replication steps

Answer 1

1.adsorption/attachment
2. entry
3. uncoating
4. genome replication and transcription
5. synthesis of virus compenents
6. assembly
7. release and maturation

Question 2

adsorption/ attachment

Answer 2

• a random collision, where an interaction between specific proteins on viral surface and specific receptors on target cell membrane (tropisms)
• not all cells carry receptors
• some viruses may have more than one host cell receptor like HIV
• viruses infect a limited spectrum of cell types - tropisms or host range
• most neutralising antibodies are specific for virion attachment proteins that block interaction with receptors and prevent entry

Question 3

entry of virus

Answer 3

penetration

• either by endocytosis or fusion of viral envelope with cell membrane

Question 4

uncoating

Answer 4

this is where the viral genome is released and host cell enzymes (lysozymes)strip off virus protein coat.
the virion can no longer be detected = eclipse period

uncoating can occur at plasma membrane, in endosomes, or at nuclear membrane

Question 5

what is a virion ?

Answer 5

A virion is the infectious particle of a virus, while the virus is the broader term that includes all forms and stages of its existence. The name “virion” helps scientists be precise about which form they’re referring to.

Question 6

assembly

Answer 6

this may take place in cell nucleus, cytoplasm or at the plasma membrane if an enveloped virus

Question 7

release of virus

Answer 7

there is a sudden rapture of the cell is non enveloped virus

or gradual extrusion- budding of enveloped virus through cell membrane

assembly may occur at same time

Question 8

viral maturation

Answer 8

this is where the new viral particles (virions) undergo changes to make then fully infectious

• structural rearrangement of viral proteins
• activation of viral enzymes or proteins
  etc

important to ensure virus is structurally complete and ready to infect new cells

Question 9

HIV maturation example

Answer 9

HIV assembles immature particles at cell membrane

after budding, HIV protease cleaves viral proteins

this triggers restructuring into a mature infectious HIV virion